Many plants are susceptible to disease caused by a variety of pests, including fungi and insects. Such pests seriously damage a crop and reduce its economic value to the grower. Crop plants are particularly vulnerable, and when disease strikes, losses can be severe. Many conventional insecticides and fungicides have detrimental effects on the environment and are implicated in human toxicity. Present methods of controlling or preventing insects and fungal disease of crop plants are unsatisfactory. A need therefore exists for new methods of protecting plants from insects and fungal disease.